Final answer:
For reliable Azure cost recommendations, the Azure documentation is the best source, offering guides and calculators for cost estimation.
Step-by-step explanation:
To find recommendations on cost optimization in Azure, the Azure documentation would be the most reliable source. It provides comprehensive guides, best practices, and calculators for estimating service costs. While the Azure Marketplace offers pricing details for various services and third-party offerings, and Azure forums can be useful for community-driven advice and experiences, the Azure support would typically assist with specific billing or technical issues. The documentation, however, is structured to give you official guidance on planning and managing your Azure spend.